Method for producing latices of copolymers of butyl acrylate and 1-methacrylate-1-tert-butyl peroxy ethane

ABSTRACT

A method for producing latices of copolymers of butyl acrylate and 1-methyacrylate-1-tert-butyl peroxy ethane resides in the emulsion copolymerization of butyl acrylate and 1-methacrylate-1-tert-butyl peroxy ethane carried out by prepolymerizing of butyl acrylate up to a conversion degree of 90-100% followed by introducing 1-methacrylate-1-tert-butyl peroxy ethane into the reaction mass. For a redox system, use is made of potassium persulfate and sodium metabisulfate.

FIELD OF THE INVENTION

The present invention relates to the production of latices of reactiverubbers, and more particularly to a method for producing latices ofcopolymers of butyl acrylate and 1-methacrylate-1-tert-butyl peroxyethane. Said compounds can be used to obtain shockproofweather-resistant copolymers and graft comb-shaped styrene copolymers aswell. Moreover, the reactive alkyl acrylate rubbers may find extensiveapplication in the production of oil- and ozone-resistant vulcanizedrubbers, the vulcanization of the rubbers can therewith be carried outwith no special vulcanizing agents added.

BACKGROUND OF THE INVENTION

Known in the art is a method for producing reactive peroxidizedcopolymers by means of mass copolymerization or suspensioncopolymerization of vinyl monomers with perester acrylates (cf. USSRInventor's Certificate No. 170,675 published in Bulletin "Otkrytia,izobretenia, promyshlennye obraztsy i tovarnye znaki", No 9, 1965, p.69). According to this method, 1-10% of monomeric peroxide is added tovinyl monomer and the reaction mixture is heated in autoclaves at atemperature ranging from 40° to 100° C. The copolymer formed comprises0.1-3% of the peroxidic groups. The copolymers obtained according tothis method have low reactivity due to a small content of the peroxidicgroups therein because of their decomposition during synthesis of thecopolymers. In further use of said copolymers to obtain graftcopolymers, their low reactivity fails to provide the grafting extentrequired.

Also known in the art is a method for producing reactive latices bymeans of copolymerization of vinyl monomers with butyl-2-acrylate-ethylperoxide (cf. a paper by Puchin V. A. et al. Syntazperekisnosoderzhashikh divinylstyrolnikh sopolymerof v emulsiyakh.Visokomoleculijrnie soedineniij. AII, 1969, No. 4, pp. 789-793). By thismethod, the copolymerization of vinyl monomers with peroxidic monomer(in amount of 1-5 mole, %) is carried out in an emulsion stabilized withammonium cetyl trimethyl bromide at temperatures of from 10° to 50° C.The copolymer formed comprises 0.1-2% of the peroxidic units.

The copolymers obtained according to this method have low reactivity dueto a small content of the peroxidic groups in the copolymers.

Known in the art is a method for producing latices of reactive alkylacrylate rubbers by means of emulsion copolymerization of alkyl acrylatewith a bifunctional acrylic monomer, such as β-chloroethyl methacrylateor glycidyl methacrylate (cf. USSR Inventor's Certificate No. 254,770published in Bulletin "Otkrytia, izobretenia, promyshlennye obraztsy itovarnye znaki", No. 32, 1969, p. 81). Copolymerization of styrene,butyl acrylate and β-chloroethyl methacrylate is carried out in emulsionat a ratio of the water phase to the hydrocarbon phase of 2:1 or 4:1, inthe presence of an emulsifier, such as sodium alkyl sulfonate, and aredox system at a reaction temperature of from 30° to 70° C. In 2-2.5hours, conversion of the monomers amounts to 95-98%.

Introduction of β-chloroethyl methacrylate units into macrochains of thebutyl acrylate rubber causes rapid aging of these rubbers. According tothis method, grafting to the butyl acrylate rubber containing chlorineatoms occurs due to the chain transfer reaction as a result of theseparation of the chlorine atom. However, low efficiency of thisreaction results in inadequate grafting of vinyl monomers to the butylacrylate rubber.

There is known a method for producing latices of alkyl acrylate rubbersused primarily in synthesizing shock-proof copolymers based on vinylmonomers (cf. USSR Inventor's Certificate No. 447,050 published inBulletin "Otkrytia, izobretenia, promyshlennye obraztsy i tovarnyeznaki", No. 31, 1976, p. 177). By this method, rubber latices areprepared by emulsion copolymerization of acrylic monomers with1-(α-alkyl acrylate)-1-tertbutyl peroxy ethanes in the presence of watersoluble emulsifiers and a reversible initiating redox system consistingof isopropyl benzene hydroperoxide, Rongalite®, and Trilon B®, thecomponents all being simultaneously introduced into the reactor.

As a result of the copolymerization, there are formed alkyl acrylaterubber latices having peroxidic side groups capable of grafting vinylmonomers.

The exothermal nature of the copolymerization of the above method (whichincreases the temperature up to 50°-60° C.) results in decomposition ofthe peroxidic groups during the latex synthesis up to 25%, whichrequires additional heat-removal.

The rubber latex, produced in accordance with the above method, exhibitslow stability stored, manifesting itself in decomposition of theperoxidic groups entering into the structure of the rubber, anddecreases the further ability of the rubber to graft vinyl monomers. Dueto such a feature, the latex cannot be used but immediately after itssynthesis.

A high rate of copolymerization in accordance with the above-mentionedmethod, namely the copolymer yield in 15 minutes amounts to 70-80%,makes it difficult to control dispersity of the latex being formed.

These disadvantages manifest themselves particularly in the cases, whenthe most available peroxidic monomer, i.e. 1-methacrylate-1-tert-butylperoxy ethane is used as 1-(α-alkyl acrylate)-1-tert-butyl peroxyethane.

SUMMARY OF THE INVENTION

The principal object of the present invention is to provide through achange in the sequence of the process steps and by a proper selection ofthe initiating redox system, a high quality end product which is stablein storage by obviating decomposition of the peroxidic groups enteringinto the copolymer structure.

With this principal object in view, there is provided a method forproducing a latex of the copolymer of butyl acrylate and1-methacrylate-1-tert-butyl peroxy ethane by emulsion copolymerizationof butyl acrylate and 1-methacrylate-1-tert-butyl peroxyethane in thepresence of an initiating redox system. According to the invention, thecopolymerization is carried out through prepolymerization of butylacrylate to a conversion degree of 90-100% followed by introducing1-methacrylate-1-tert-butyl peroxy ethane into the reaction mass,potassium persulfate and sodium metabisulfite being used as theinitiating redox system.

It is expedient to introduce the initial monomers stepwise to adjust thelatex particle diameter.

Best Mode for Carrying out the Invention

The proposed method for producing a latex of the copolymer of butylacrylate and 1-methacrylate-1-tert-butyl peroxy ethane is carried out asfollows.

The emulsion copolymerization of the initial monomers is carried out ina reaction vessel thermostated at 20° C. and provided with a stirrer,return condenser, and an inert gas feeding tube. pH of the reactionmixture is maintained within the range of 7.5-9.0.

For emulsifiers, use is made of surface-active anionogens, for examplesodium salts of fatty sulfacids (alkyl sulfonates having hydrocarbonradicals of C₁₂ H₂₅ to C₁₈ H₃₇).

The reactive vessel is charged with water, emulsifier, pH-adjuster,namely borax (Na₂ B₄ O₇.10 H₂ O).

Upon dissolution of the emulsifier and borax in the reaction vessel,there is introduced, under stirring, butyl acrylate followed byemulsification and purging the reactive mixture with an inert gas for 10minutes. Next, there are introduced the components of the initiatingsystem, namely potassium persulfate and sodium metabisulfite, and thereaction proceeds with a continuous flow of the inert gas. In four hoursafter the start of the reaction (from the moment of introducing theinitiating system) when 90-100% of the butyl acrylate is converted, thesecond portion of the monomeric mixture consisting of butyl acrylate and1-methacrylate-1-tert-butyl peroxy ethane is introduced. In five hoursfrom the start of the reaction the third portion of the monomericmixture similar to the second portion is added. To permit adjustment ofthe latex particle diameter, adding of the butyl acrylate can beperformed stepwise with small portions. In six hours the reaction iscompleted.

The proposed method exhibits a number of advantages as compared to theknown methods.

The proposed method, due to introducing the peroxidic comonomer atsuccessive stages of the reaction, and hence, due to its decreasedexposure in the reaction zone, ensures practically complete retention ofthe peroxidic groups in the rubber obtained.

Said method results in a concentrating of the peroxidic groups in thesurface zone of the latex particle, which increases the efficiency ofgrafting vinyl monomers on to the rubber particle, when synthesizingshockproof copolymers.

When synthesizing latices, the use of the initiating redox system ofpotassium persulfate K₂ S₂ O₈ and sodium metabisulfite Na₂ S₂ O₅ inconjunction with successive introduction of the reaction mixturecomponents, makes it possible to readily adjust the reaction rate,preventing the temperature increase on the stages of introducing theperoxidic copolymer above 25° C.

The possibility of varying the order of introducing the componentsenables adjustment of the latex particle size over a wide range(0.05-0.25 micron), the latices formed having a high aggregativestability despite the use of small amounts of the emulsifier.

The latices obtained by this method enjoy high stability manifestingitself in that practically no decomposition of the peroxidic groupsoccurs during long-term storage of the latex at room temperature.

Characteristic examples illustrative of the implementation of theproposed method for producing a latex of the copolymer of butyl acrylateand 1-methacrylate-1-tert-butyl peroxy ethane according to the presentinvention are given below.

EXAMPLE I

500 g of water (110 parts by weight), 7.5 g (1.66 parts by weight) ofthe mixture of alkyl sulfonates having a hydrocarbon radical of C₁₂ H₃₇to C₁₈ H₃₇, 1.90 g (0.42 parts by weight) of borax (Na₂ B₄ O₇.10 H₂ O)are introducted into a reaction vessel thermostated at 20° C. andprovided with a stirrer, a return condenser, and an inert gas feedingtube.

Upon dissolution of the emulsifier and borax, the reactor is charged,under stirring, with 360 g (79.6 parts by weight) of butyl acrylate,followed by emulsification and purging of the reaction mixture with aninert gas for 10 minutes. Next, the components of the initiating systemare introduced, namely 1.56 g (0.34 part by weight) of a potassiumpersulfate and 0.729 g (0.16 part by weight) of sodium metabisulfite,the reaction being carried out in a flow of the inert gas. In four hoursfrom the start of the reaction (from the moment of introducing theinitiating system), upon 90% conversion of the butyl acrylate introduced22 g (4.9 parts by weight) of butyl acrylate and 24 g (5.3 parts byweight) of 1-methacrylate-1-tert-butyl peroxyethane are added. In fivehours from the start of the reaction, another 22 g (4.9 parts by weight)of butyl acrylate and 24 g (5.3 parts by weight) of1-methacrylate-1-tert-butyl peroxy ethane are added. In six hours thereaction is completed.

The resulting latex of copolymer of butyl acrylate and1-methacrylate-1-tert-butyl peroxy ethane has the followingcharacteristics:

dry residue 44% of the latex mass

average particle diameter 0.055 μm

content of the peroxidic monomer units in the copolymer 9.9% by weight.

When storing the latex at room temperature for 30 days no change in thecontent of the active oxygen occurs, which is indicative of nodecomposition of the peroxidic groups and the stability of thecopolymer.

EXAMPLE 2

500 g (110 parts by weight) of water, 7.5 g (1.66 parts by weight) ofthe mixture of sodium alkyl sulfonates having a hydrocarbon radical ofC₁₂ H₂₅ to C₁₈ H₃₇, 1.90 g (0.42 part by weight) of borax (Na₂ B₄ O₇.10H₂ O) are mixed in a reaction vessel thermostated at 20° C. and providedwith a stirrer, a reflux condenser, and an inert gas feeding tube.

Upon dissolution of the emulsifier and borax, the first portion of butylacrylate of 180 g (20 parts by weight) is introduced, under stirringinto the reactor, followed by emulsifying and purging the reactionmixture with an inert gas for 10 minutes. The reactor is then chargedwith the initiating system containing 2.45 g (0.27 part by weight) ofpotassium persulfate and 1.21 g (0.13 part by weight) of sodiummetabisulfite, the reaction being carried out for 1 hour in a flow ofthe inert gas, whereupon the second portion of butyl acrylate of 180 g(20 parts by weight) is added.

In two hours from the start of the reaction, the third portion of butylacrylate of 180 g (20 parts by weight) is introduced, and in threehours, the fourth portion of 180 g (20 parts by weight) is added. Infour hours from the start of the reaction, upon 90% conversion of thebutyl acrylate introduced, 90 g (10 parts by weight) of butyl acrylateand 90 g (10 parts by weight) of 1-methacrylate-1-tert-butyl peroxyethane are introduced. In five hours the synthesis is completed.

The resulting latex has the following characteristics:

dry residue 45% of the latex mass

average particle diameter 0.20 μm

content of the peroxidic monomer units in the copolymer 9.6% by weight.

When storing the copolymer latex at room temperature for 30 days, nochange in the content of active oxygen occurs.

EXAMPLE 3

Both the charge volume and order of introducing the first four portions(180 g each) of butyl acrylate are similar to those indicated in Example2.

In four hours from the start of the reaction, upon 100% conversion ofthe butyl acrylate charged, and then in 4.5 hours, 5 hours and 5.5 hoursfrom the start of reaction, in succession four portions (45 g i.e. 5parts by weight each) of 1-methacrylate-1-tert-butyl peroxy ethane areintroduced. In 7 hours the synthesis is completed.

The latex thus produced has the following characteristics:

dry residue 43% of the latex mass

average particle diameter 0.25 μm

content of the peroxidic monomer units in the copolymer 18.6% by weight

When storing the copolymer latex at room temperature no change in thecontent of active oxygen occurs.

EXAMPLE 4 (CONTROL)

The synthesis of a latex of the copolymer of butyl acrylate and1-methacrylate-1-tert-butyl peroxy ethane is carried out using thefollowing initiating redox system consisting of isopropyl benzenehydroperoxide, Rongalite®, Trilon B®, the total mass of butyl acrylateand 1-methacrylate-1-tert-butyl peroxy ethane being introduced at atime.

Formula for preparing the latex:

butyl acrylate 330 g (90 parts by weight)

i-methacrylate-i-tert-butyl peroxyethane 33 g (10 parts by weight)

isopropylbenzene hydroperoxide 0.26 g (0.8 part by weight)

Rongalite® 0.333 g (0.10 part by weight)

Trilon B® 0.033 g (0.01 part by weight)

alkyl sulfonate 4.99 g (1.5 parts by weight)

water 666 g (200 parts by weight)

The temperature of the reaction mixture increases up to 60° C. duringthe synthesis process.

The latex thus produced has the following characteristics:

dry residue 33% of the latex mass

average particle diameter 0.06 μm

content of the peroxidic monomer units in the rubber 7.5% by weight.

When storing the latex at room temperature, the content of the peroxidicmonomer units free of decomposition is lowered to 6.0% by weight in 30days, to 4.1% by weight in 90 days, which evidences a low stability ofthe copolymer latex with regard to storage.

INDUSTRIAL APPLICABILITY

Thus, the proposed method makes it possible to improve the process forproducing latices of reactive butyl acrylate rubbers, enables maximumpreservation of the groups in the rubber when synthesizing and storingthe latex, ensures adjustment of the latex particle size over a widerange (0.05-0.25 μm) and makes it possible to concentrate the peroxidicgroups in the surface zone of the rubber particles, which results in anincreased efficiency in grafting vinyl monomers on rubber.

The proposed latices can be used to best advantage, for example, in thesynthesis of weather-resistant ABS-plastics due to the decreased latexvolume as a result of high content of the peroxidic units in the rubber,which results in considerable saving in the initial material.

We claim:
 1. A method for producing latices of copolymers of butylacrylate and 1-methacrylate-1-tert-butyl peroxy ethane by emulsioncopolymerization of butyl acrylate and 1-methacrylate-1-tert-butylperoxy ethane in the presence of an initiating redox system,characterized in that the copolymerization is carried out throughprepolymerization of butyl acrylate up to a conversion degree of 90-100%followed by introduction of 1-methacrylate-1-tert-butyl peroxy ethaneinto the reaction mass, potassium persulfate and sodium metabisulfitebeing used as the initiating redox system.
 2. A method according toclaim 1, characterized in that the initial materials are introducedportion-wise.